This is a interesting one. I once heard a psychiatrist ask someone during an evaluation: have you ever borrowed Ritalin from your friends? Follow up question: did it work?

I guess this is a really nice hack he had: Has used Ritalin illegally? Increased probability of ADHD. Does it work? Even more increased probability and he know knows the person tolerates it.

This fascinates me. Some people seriously take stimulants at night to fall asleep, others in the morning to wake up..!

Recently I heard the story about how stimulants came to be used to treat ADHD and one thing that stood out except that this was an extremely suprising effect was the very simplified explanation that stimulants seems to stimulate the inhibitory parts of the brain most which seems to account for the increased self control.